diff options
Diffstat (limited to 'src/device/pci_device.c')
| -rw-r--r-- | src/device/pci_device.c | 39 |
1 files changed, 39 insertions, 0 deletions
diff --git a/src/device/pci_device.c b/src/device/pci_device.c index 0a4b69bfb2..191c8460c8 100644 --- a/src/device/pci_device.c +++ b/src/device/pci_device.c @@ -793,6 +793,43 @@ struct device_operations default_pci_ops_bus = { }; /** + * Check for compatibility to route legacy VGA cycles through a bridge. + * + * Originally, when decoding i/o ports for legacy VGA cycles, bridges + * should only consider the 10 least significant bits of the port address. + * This means all VGA registers were aliased every 1024 ports! + * e.g. 0x3b0 was also decoded as 0x7b0, 0xbb0 etc. + * + * To avoid this mess, a bridge control bit (VGA16) was introduced in + * 2003 to enable decoding of 16-bit port addresses. As we don't want + * to make this any more complex for now, we use this bit if possible + * and only warn if it's not supported (in set_vga_bridge_bits()). + */ +static void pci_bridge_vga_compat(struct bus *const bus) +{ + uint16_t bridge_ctrl; + + bridge_ctrl = pci_read_config16(bus->dev, PCI_BRIDGE_CONTROL); + + /* Ensure VGA decoding is disabled during probing (it should + be by default, but we run blobs nowadays) */ + bridge_ctrl &= ~PCI_BRIDGE_CTL_VGA; + pci_write_config16(bus->dev, PCI_BRIDGE_CONTROL, bridge_ctrl); + + /* If the upstream bridge doesn't support VGA16, we don't have to check */ + bus->no_vga16 |= bus->dev->bus->no_vga16; + if (bus->no_vga16) + return; + + /* Test if we can enable 16-bit decoding */ + bridge_ctrl |= PCI_BRIDGE_CTL_VGA16; + pci_write_config16(bus->dev, PCI_BRIDGE_CONTROL, bridge_ctrl); + bridge_ctrl = pci_read_config16(bus->dev, PCI_BRIDGE_CONTROL); + + bus->no_vga16 = !(bridge_ctrl & PCI_BRIDGE_CTL_VGA16); +} + +/** * Detect the type of downstream bridge. * * This function is a heuristic to detect which type of bus is downstream @@ -1293,6 +1330,8 @@ void do_pci_scan_bridge(struct device *dev, bus = dev->link_list; + pci_bridge_vga_compat(bus); + pci_bridge_route(bus, PCI_ROUTE_SCAN); do_scan_bus(bus, 0x00, 0xff); |